The present invention relates to a voice modifier, and more particularly relates to a voice modifier which can transpose or distort one voice into another voice by receiving the input audio signals with normal frequency and transmitting the output audio signals with different or unusual frequencies.
Heretofore, the concepts involving speech sampling and companding, and the variation of the frequencies in clock signals have been developed in many parts of the world. For example, U.S. Pat. No. 4,682,362 to DeFreitas et al., entitled "Generating Narrowly-separated Variable-frequency Clock Signals", discloses circuitry for generating clock signals of slightly different frequencies in which an analog to digital converter, a memory and a digital to analog converter are provided. A primary objective of the prior art is to produce a flange effect between the analog output signal and input signal. This is achieved by the employment of at least one of the clocks having a variable frequency provided by a voltage-to-frequency converter driven by the output of an integrator, which is supplied with the sum of a frequency-difference-command signal (supplied by a supervising microprocessor) and a difference signal representative of the actual difference in frequency between the two clocks. Data is written into memory at the address specified by encoding pointer, and data is read from the memory at the address specified by decoding pointer. It should be noted that the speed of the encoding pointer is set by fixed encoding clock and is constant; changes in delay are brought about by slightly varying the decoding clock relative to the encoding clock, under control of a microprocessor. Comprehensively, the decoding pointer has to trail behind the encoding pointer by the time period of the delay; moreover, the longer the of delay is, the more memory capacity is needed to store the signals.
Unlike the prior art, which discloses circuitry to control the clocks in a system for providing variable delay of an audio signal, the encoding pointer and decoding pointer used in the present invention are independent and different to produce a transposing or distorting effect on audio signal. The features of this invention can be easily realized by explaining the operation of a phonograph.
As is well known, if a phonograph record is played at 331/3 RPM, it will create a much different effect than if it is played at 45 RPM. So obviously, one means of modifying the quality of a voice would be to transmit the audio signals at a frequency higher or lower than the receiving frequency, for example, twice or half the receiving frequency. For the purpose of further understanding the teaching of this invention, the basic concept and basic block diagram thereof are shown hereinafter with brief description.
FIG. 1A is a graph illustrating the relation between voltage and time of an input signal waveform, and FIG. 1B is a similar graph with a transmitting frequency equal to twice the transmitting frequency of FIG. 1A. When at time T, the position of voltage of FIG. 1B with respect to time is equivalent to the position of voltage of FIG. 1A corresponding to time 2T.
More specifically, FIG. 2 schematically illustrates a signal process for a voice modifier comprising an analog to digital (A/D) converter 62 which converts an analog signal 61 into a digital signal, a memory unit 63 which stores the digital signal, a digital to analog (D/A) converter 64 which converts the stored digital signal into an analog signal, and an amplifier 65. The voice modifier has a transmitting frequency f2 higher/lower than the receiving frequency f1 so that the output signal is different from the input signal.
The concepts of over-write and over-read are involved in this invention to solve the demand of an infinite memory when the encoding pointer is far ahead the decoding pointer (i.e., receiving frequency&gt;&gt;transmitting frequency) and the stack of digital signals being stored is increasing with time, since the decoding pointer is independent from the encoding pointer. Moreover, a continuous variable-slope delta modulation (CVSD), adaptive delta modulation (ADM), or delta modulation (DM) system is employed in this invention for designing D/A and A/D converters to smooth the discontinuous portions resulting from over-write or over-read.